This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2000-93966 filed on Mar. 30, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a pressure regulation valve whose output pressure variable characteristics that is changed over between pressure proportional to pilot pressure and pressure equal to supply pressure.
2. Description of Related Art
Conventionally, as shown in FIG. 7, is known a hydraulic circuit system having a pressure regulation valve 107 for adjusting output pressure to be applied to a hydraulic circuit 101 into control pressure proportional to pilot pressure. The hydraulic circuit 101 communicates with a hydraulic servo 100 for driving a hydraulic engagement member constituting a hydraulic multiple disk clutch (hereinafter called clutch) which serves to engage components with each other in a planetary gear device arranged between an input and output axes of a vehicle automatic transmission.
The hydraulic circuit system is provided with a pilot pressure control valve 104 driven by a solenoid valve 103, a shift valve whose valve position is shifted upon receiving modulator pressure output from a modulator valve 105, and a pressure regulation valve 107 for adjusting output pressure. The solenoid valve 103 is composed of a solenoid coil 131, a coil bobbin 132, a stator core 133, a moving core 134, a solenoid shaft 135, a yoke 136, a plate spring 137 and a cover 138.
The pilot pressure control valve 104 has a spool 141 that is slidably housed in a valve body 110 and moves to communicate a pilot pressure conduit 111 either with a conduit 112, to which modulator pressure from the modulator 105 is applied, or with a conduit 113, which communicates with a drain 109. One end of the spool 141 receives force from the solenoid valve 103 upon its operation and the other end of the spool 141 is urged in an opposite direction to which force from the solenoid valve 103 is applied by biasing force of a spring 143 whose one end is held by the other end of the spool 141 and whose another end is held by a plug 142.
The shift valve 106 has a spool 161 that is slidably housed in the valve body 110 and serves to change the output pressure to be applied to the pressure regulation valve 107. The spool 161 is urged in a direction opposite to receiving pilot pressure to be input into a pilot pressure feedback chamber 164 by biasing force of a spring 163 whose one end is held by a stopper 162 and whose another end is held by the spool 161. A conduit 165 is a drain port communicating with the drain 109. The other end of the spool 161 receives the modulator pressure through the conduit 112.
The pressure regulation valve 107 has a spool 171 that is slidably housed in the valve body and moves so that the hydraulic circuit 101 communicates with a conduit 114 for a pressure supply source 102 or with a conduit 115 for the drain 109. The spool 171 is urged in an opposite direction to which the pilot pressure is applied by biasing force of a spring 173 whose one end is held by the spool 171 and whose another end is held by the valve body 110. Conduits 174 and 175 are drain ports communicating with the drain 109. The other end of the spool 171 receives the output pressure from the shift valve 106.
In the conventional hydraulic circuit system mentioned above, the pressure regulation valve 107 adjusts the output pressure (pressure to the clutch) either to pressure proportional to the pilot pressure at a time of clutch engagement control during which it is required to accurately control pressure to be applied to the servo 100 for driving the clutch or to higher pressure with which the clutch never slides even if higher torque is applied thereto at a time after the clutch engagement control.
In more details, according to increase of the pilot pressure input to the pilot pressure feedback chamber 164, the spool 161 of the shift valve 106 moves toward a left side in FIG. 7 so that the drain port 165 is opened and the output pressure of the shift valve 106, which the other end of the spool 171 of the pressure regulation valve 107 receives, becomes zero. Accordingly, the spool 171 moves rapidly up to a left end in FIG. 7 so that pressure equal to higher pressure from the pressure supply source 102 is applied to the hydraulic circuit 101.
Since the conventional hydraulic circuit system has the pilot pressure control valve 104 and the shift valve 106 in addition to the pressure regulation valve 107, an entire body thereof becomes larger.
Further, there is another conventional system having a pressure regulation valve whose pressure amplitude ratio is remarkably high so that higher pressure is secured at a time after the clutch engagement control. However, in this system, it is very difficult to accurately and precisely control the pressure to the clutch, which results in adversely affecting on driving feeling at a time of transmission stage change.
An object of the invention is to provide a compact pressure regulation valve for a hydraulic circuit in which an output pressure is accurately regulated to pressure proportional to pilot pressure at a relatively low pressure region where linear pressure control is required and to pressure directly supplied from a pressure supply source at a relatively high pressure region where maximum pressure is required.
To achieve the above object, a pressure regulation valve for a hydraulic circuit is composed of a housing having an input port to communicate with a supply pressure source, an output port to communicate with the hydraulic circuit and at least a drain port to communicate with a drain, a pilot pressure producing member supplying pilot pressure, which increases from zero to a value exceeding a given value, to the housing, a pipe shaped first spool accommodated slidably in the housing so as to receive the pilot pressure, a first biasing member giving the first spool biasing force acting in an opposite direction to receiving the pilot pressure, a feedback hydraulic chamber provided in the housing, a second spool accommodated slidably inside the first spool so as to receive the pilot pressure, and a second biasing member giving the second spool second biasing force acting in an opposite direction to receiving the pilot pressure.
With the pressure regulation valve mentioned above, the first spool is moved in the housing by first thrust force due to the pilot pressure so that the output port communicates internally with the drain port, when the pilot pressure is substantially zero, and communicates internally with the input port, when the pilot pressure exceeds the given value.
Further, the second spool is movable in the first spool by second thrust force due to the pilot pressure so that the feedback hydraulic chamber communicates internally with the output port, when the pilot pressure is below the given value, and communicates internally with the drain port, when the pilot pressure exceeds the given value.
Furthermore, the feedback hydraulic chamber gives the first spool feedback force acting in an opposite direction to which the first spool receives the pilot pressure when the feedback hydraulic chamber communicates with the output port.
The first spool moves in the housing to a position where the first thrust force balances with a sum of the first biasing force and the feedback force. When the pilot pressure is within a range from substantially zero to the given value, a normal output pressure proportional to the pilot pressure is supplied from the output port to the hydraulic circuit, since the feedback hydraulic chamber communicates with the output port and the feedback force is given to the first spool.
When the pilot pressure is in a range exceeding the given value, a maximum output pressure equal to supply pressure of the supply pressure source, which-is higher by a predetermined value (for example, 0.7 Mpa) than the normal pressure, is supplied from the output port to the hydraulic circuit, since the feedback hydraulic chamber communicates with the drain so that the feedback force becomes zero and the first spool further moves to a position where the input port communicates with the supply pressure source.
As the pressure regulation valve has the second spool housed in the first spool for controlling the movement of the first spool, an entire body constituting the hydraulic circuit becomes compact and results in less manufacturing cost.
Further, to make the entire body of the hydraulic circuit more compact, it is preferable that the pilot pressure producing member is a pilot pressure control valve being provided with a third spool that is arranged coaxially with the first spool and a valve housing formed integrally with the housing.